Method and apparatus for digital data processing



June 11, 1968 T. R. FOLSOM ET AL METHOD AND APPARATUS FOR DIGITAL DATA PROCESSING Filed April 16, 1964 INVENTORS THEODORE R. FOL $0M AGEN T ATTORNEY RICHARD A. CRAMER United States Patent 3,388,377 METHOD AND APPARATUS FOR DIGITAL DATA PROCESSING Theodore Robert Foisom and Richard A. Crarner, La

Jolla, Calif., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Apr. 16, 1964, Ser. No. 360,466 1 Claim. (Ci. 340-1461) ABSTRACT OF THE DISCLOSURE A signal processing system for recovering repetitive signals from noise. System synchronized to divide signal interval into many segments, each of which is associated with a storage device that is sequentially connected into the system. Signal segments are digitalized by converter and predetermined number of digitalized segments are summed in each storage device. Storage devices are scanned and contents displayed in analog form. Provisions are also included to display change between present display and prior displays.

This invention relates to method and apparatus for analyzing data and in particular to method and apparatus for recovering signals from noise in electronic detection systems.

In any electronic detection system the capability of distinguishing between the desired signal and undesired background noise is the limiting factor in the sensitivity of the system and is therefore of major importance. This invention relates to a technique, and apparatus for practicing the technique, of separating the desired signal from undesired random background noise and thereby extending the lower useful signal limit of the various detection apparatuses which are capable of being used together with the data analyzing features of this invention. These vari ous compatible apparatuses, while limited to those wherein the desired signal occurs periodically, are Well known in such widely diversified fields as radar, sonar, nondestructive testing, radio astronomy, television, medicine, fiuid flow measuring and many others.

It is, therefore, an object of the present invention to provide a method and apparatus for separating a recurring signal from random background noise.

Another object is to provide a method and apparatus for increasing the sensitivity of electronic detection systerns.

Still another object is to provide a method and apparatus wherein data is accumulated in digital form in such a manner that a recurring signal is emphasized by addition whereas random noise is not emphasized and becomes obscured.

Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following description of an embodiment of the invention as illustrated in the accompanying sheetor" drawing which is a block diagram of the invention.

According to the present invention, the incoming data to be analyzed, which includes both the periodically recurring desired signal and random noise, is separated into intervals such that the desired signal occurs at relatively the same time position in each interval, or in other words, the interval and signal frequencies are either equal or related by an integral factor. During each interval the amplitude is sensed at a plurality of time positions and converted from analog to digital form. The digital information relating to each of the plurality of time positions in an interval is combined with the digital information from each of the plurality of time positions from other intervals, that is,

the digital information relating to the first, second, third,

etc. time positions in a first interval is additively combined with the digital information relating to the first, second, third, etc. time positions in following intervals.

After the digital information has been combined for a predetermined number of intervals, the combined digital information for the plurality of time positions is converted to analog form and displayed in trace form representative of a composite of the predetermined number of intervals. Because of the random nature of the noise, the noise will tend to be smothed out over the entire trace of the composite interval, whereas the repetitive desired signal will be emphasized. Thus, by combining a single interval, wherein the desired signal may be indiscernibly buried in the random noise, with a predetermined number of other intervals, the desired signal will become apparent as the random noise is obscured.

Depending upon the purpose of the detecting system, it may be desirable to include in the invention means to record the trace of the composite interval and to compare this trace with previous composite traces and to provide a warning in the event of a significant difference between the present and previous composite traces.

It is to be noted that the intermediate procuring of the data in digital, rather than analog, form advantageously provides for a system having high accuracy and driftfree stability.

Referring now to the drawing, wherein the invention is illustrated in block diagram form, it is to be recognized that the operation of the various components are synchronized by electronic controls, which preferably function by means of short duration voltage pulses. Such electronic controls are well known and, for the purpose of simplifying the drawing, have been illustrated to only a limited extent.

Information to be analyzed is received by component 11 and is displayed in the single interval form on device 12, such as a conventional CRO tube, which is under the control of synchronizing oscillator 13. As is indicated in the drawing, synchronizing oscillator 13 also synchronizes and controls the operation of other components.

When the incoming information is related to signals which have their origin in periodically transmitted pulses, as in a radar detection system, the synchronizing oscillator 13 conveniently can be the master oscillator of the transmitter. If, however, the frequency of the desired incoming signal varies, as may occur in the so-called sing around loop ultrasonic fiowrneters, the frequency of the trolled to be integrally related to the frequency of the desired signal. Such control would, of course, also result in the desired single interval being displayed on device 12.

The information signal to be analyzed, after any necessary amplification in component 11, is connected to an analog-to-digital converter (ADC) 14 which is in turn connected to memory channel selector (MSC) 15. Both the ADC and MCS are under the control of pulse generator 16 which functions to produce in control pulses for each pulse generated by synchronizing oscillator 13. The ADC is energized by each control pulse from generator 16 to furnish a digital count, or series of pulses, related to the instantaneous value of the information signal to be analyzed. Expressed in a dilferent view, for a single interval, the ADC 14. under the control of n pulses from generator 16, divides the display on device 12 into n increments or time positions and furnishesa digital output for each increment or time posit-ion.

The MCS 15, which is also energized by the pulses from generator 16, sequentially enters each of the n incremental counts into an :1 channel memory device '17 where the digital counts are accumulated for a predetermined number of intervals. At the end of the predetermined number of intervals, each one of the 11 memory channels will have accumulated a count equal to the sum of a predetermined number of digital counts associated with a particular time position. In other words, a memory channel in device 17, say the 23rd channel, will have accumulated a digital count equal to the sum of the incremental counts by ADC 14 related to the 23rd time position for a predetermined number of intervals.

After the predetermined number of intervals, which should be sufiicient for a Smoothing out of the random noise, the digital counts in the n channel memory device 17 are read out by means of digital-to-analog converter 18 and the resultant, or composite, trace is displayed on device 19, which conventiently can be a conventional CRO tube.

It will be recognized that the composite trace displayed on device 19 is such as to be compatible with the single interval trace on display device 12. In other words, if the time positions 1, 2, 3 n are sequentially arranged from left to right on the trace displayed by device 12, i

the digital count in the memory channels 1, 2, 3 n of device '17 are similarly displayed in analog form from left to right in the display on device 19.

It has been found that, because of the random nature of the noise, in a composite trace of a predetermined number of intervals, for instance 100 intervals, the random noise etfects will be averaged out or obscured whereas the repetitive signals will be relatively emphasized. Thus, while the desired signal may be obscured by noise in the single interval trace displayed on device 12, the composite trace displayed on device 19 will quite clearly present the desired signal. Further, because of the stability of the digital form of processing, the relationship between the trace displayed on device 19 and the strength of the desired signal will be quite linear, even though the signal strength would normally, when considered on a single interval basis, be much below the operable threshold of the detection system. In other words, by using the composite trace on device '19, an operator would be able to recognize signals which would ordinarily be below the sensitivity level of the detection system.

With certain detection systems, such as early warning radar, it may be desirable to observe and record changes in the composite trace displayed on device 19. This can be accomplished if, in conjunction with the read out of i the predetermined interval count from memory device 17, the accumulated counts are transferred from device 17 to a similar memory device 20, thereby clearing memory device 17 preparatory of receiving the digital counts relating to a next predetermined number of signal intervals. Device 20 will, of course, be cleared of previously stored digital counts prior to receiving the current counts from device 17.

The memory device 20 is connected to a digital-toanalog converter 21, which is in turn connected to a commer-cial-ly available CRO display device 22 that is characterized by the ability to present traces representative of the 10 most recent read outs of memory device by digital-to-analog converter 21. A recorder 23 is also connected to the digital-to-analog converter 21 to provide a permanent record of each of the composite traces.

A conventional analog difference amplifier 24 is connected to the outputs of digital-to-analog converters 18 and 21. The output of amplifier 24 is connected to CRO display device 25, recorder26 and warning device 27 to thereby display and record a trace representative of the difference between the present and the previous composite traces and to sound an alert in the event the difference exceeds a predetermined amount. It is, of course, evident that the comparator could take the form of a digital comparator and be connected to memory devices 17 and 2% to provide channel by channel comparison of the current and previous composite counts. With such a comparator, an additional digital-to-analog converter would be required.

All of the components above described are either so Well known as to require no further description or are commercially available. For example, the memory channel selector 15 amounts to no more than an electronic switch and the analog-to-digital converter 14 is widely known and utilized in such common devices as digital voltmeters. The ten trace display device 22 is commercially available as a Huges Co. Memo-scope and units suitable for use as the n channel memory devices 17 and 20 and the digital-to-analog converters 18 and 21 are commercially marketed by Radiation Counter Laboratories, Inc.

The operation of the invention in an early warning radar detection system will now be described, although as previously emphasized, the utility of the invention is obviously not confined to such a limited use.

In early warning radar, the most important function of the detection system is evaluating electromagnetic wave reflections from distant objects. These reflections,

ecause of the distance of the target, are often so weak as to be indiscernibly mixed with random, or background, noise. This invention, when used with early warning radar, would extend the operable distance range of the detection system by causing target signals, ordinarily obscured, to be identifiable.

In a radar detection system the component 11 would be the radar atenna and receiver, the single interval display 12 would be the A scan scope and the oscillator 13 would be the master oscillator of the radar set, so that no adjustment of the frequency of synchronizing ocsillator 13 would be necessary.

The incoming signals are processed in the desirable digital form and stored, as previously described, by components 14-17. Excellent results were obtained in a prototype wherein n was made equal to 256. The generator 16, therefore, generated 256 pulses for each pulse from the oscillator 13 and energized ADC 14 to, in effect, separate a single interval into 256 time positions and to evaluate by digital signal the amplitude at each time position. Generator 16 also controlled MCS 15 to sequentially route the time position signals into the 256 memory channels in device 17. Each memory channel in the prototype was capable of a 16 digit binary count, or of a decimal count of 65,535.

Digital counts representing signal intervals were grouped in the composite trace displayed on display device 19. Since in the prototype a single interval A scan sweep occurred 10 times a second, a composite trace on device 19 and a difference, or change, trace on device 25, were displayed once every 10 seconds. The 10 traces shown on the Memo-scope 22, therefore, presented to the operator a visual 100 second history of the incoming signal. Both the difference trace displayed on device 25 and the 10 trace presentation on device 22 give the operator an indication of the movement of the target.

It is apparent that a method and apparatus using digital processing has been disclosed for separating a recurs ring signal from random background noise and thereby increasing the sensitivity of electronic detection systems.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically claimed.

What is claimed is:

1. Apparatus for analyzing data which includes a repetitive signal obscured by random noise comprising: data input means; a synchronizing oscillator producing pulses at a frequency related to the repetition rate of said signal; a pulse generator producing pulses at n times the frequency of the pulses produced by said synchronizing oscillator where n is an integer greater than one; an analog-to-digital converter connected to said data input means and energized by each pulse from said pulse generator to produce a digital signal related to the instantaneous amplitude of said data; a first 11 channel memory device capable of additively storing digital signals in each of n channels; a selector device connected to said analogto-digital converter and energized by the pulses from said pulse generator to sequentially connect said analog-todigital converter to each of then channels in said first memory device; read out means connected to said first memory device to provide an output representative of the digital signals stored in said first n channel memory device, said read out means including a first digital-toanalog converter connected to said first memory device and a first display device connected to said first digitalto-analog converter for displaying said representative output in trace form; change indicating means for indicating the change occurring in said representative output, said change indicating means including a second 11 channel memory device connected to said first memory device, a second digital-to-analog converter connected to said second memory device, comparator means which indicates the difierence between the output of said first and second digital-to-analog converters, a second display device connected to the output of said comparator means for displaying said difference in trace form, and a warning device connected to the output of said comparator means to sound an alert in event said difference exceeds 6 a predetermined amount; and a multiple trace display device connected to said second digital-to-analog converter for displaying a plurality of previous traces from representative outputs.

References Cited UNITED STATES PATENTS 2,659,078 11/1953 Sherr 3437.7 2,882,525 4/1959 Young 3435 2,902,644 9/1959 McDonald 32477 3,153,699 10/1964 Plass 1786.8 3,299,205 1/1967 Stavis 1786.8 3,065,464 11/1962 Sullivan 34313 3,087,487 4/1963 Clynes 1282.1 3,142,822 7/1964 Martin 340173 3,147,373 9/1964 Clynes 235181 3,209,322 9/1965 Doty 34015.5 3,284,616 11/1966 Ernyee et al. 235150.5

OTHER REFERENCES M. Clynes: CAT; Instruments and Control Systems; August 1962, pages 8791.

MALCOLM A. MORRISON, Primary Examiner.

K. F. MILDE, V. SIBER, Assistant Examiners. 

